1. Field of the Invention
Using induction heaters, two rotating metal bands are heated to a target temperature, continuously sensed by infrared temperature probes and then compressed on either side of a mated pair of paperboard carton flanges in an extended nip. The mated paperboard flange area is then heated by conduction from the metal bands to the activation temperature of the coating material to form a uniform bond between the paperboard surfaces.
2. Description of the Related Art
It is known, in packaging apparatus, to employ various equipment for sealing film material to trays. Exemplary of such prior art are U.S. Pat. No. 3,436,894 ('894) to R. P. Sorensen, entitled "Packaging Apparatus and Method" and U.S. Pat. No. 3,416,292 ('292) to O. R. Weber, entitled "Apparatus for Making Covered Receptacles or The Like". While the '894 and '292 references disclose a continuous sealing method, the '894 reference relies on heating a contoured wheel or drum unit via conventional heating elements and the '292 reference discloses using belts which are heated via the conduction of heat from the carrier rollers. However, such broad applications of heat through the use of the belts or wheels/drum units can create a marring of the lid, which is unacceptable to the customer.
It is also known in the packaging of paperboard cartons to employ induction sealing. Exemplary of such prior art are U.S. Pat. No. 4,637,199 ('199) to R. F. Steck et al., entitled "Induction Sealing of Paperboard" and U.S. Pat. No. 5,117,613 ('613) to G. D. Pfaffmann, entitled "Induction Heating and Packaging Sealing System and Method". While the '199 and '613 references disclose induction heating, the material to be sealed must have a metallic layer to carry the current produced and heat the sealant layer. A more advantageous system, then, would be presented if such a metallic layer could be eliminated.
It is apparent from the above that there exists a need in the art for a paperboard carton system which is capable of sealing paperboard cartons while reducing the marring of the carton, but which at the same time substantially eliminates the need for any metallic layers in the paperboard carton.
It is a purpose of this invention to fulfill this and other needs in the art in a manner more apparent to the skilled artisan once given the following disclosure.